I have a 2003 Chevy 1500 (RWD) with about 120K miles on it. Several days ago, I noticed that at around 30 mph it shakes a bit. The shakes seam to be coming from the rear of the truck. This shaking does not occur at 20 mph or 40 mph. Just 30 mph +/- 5 mph. So, is this just something wrong with my tires or is there a more serious issue? I'm thinking about taking it to a shop but am curious about what this could be. There does tend to be some sort of noise associated with this problem. Can't pinpoint what it is. For now, my wife isn't allowed to drive it. EDIT 1: OH, When I'm braking at very low speed (10 mph even) there seems to be some sort of problem related to the shaking that is also new. Recently, I rotated my tires and checked the brake pads and they have plenty of life left in them. The rear rotors are new (10K miles) and the front are original to the truck (thinking about replacing them soon just as preventative maintenance). Since the rear rotors are newer and the pads are fine I have a hard time believing that the shaking which seams to be coming from the rear is brake related. EDIT 2: This also happens at very low engine RPM (1300 maybe). I haven't checked to see if this is evident at a faster speed and low engine RPM. But when braking at 10 mph, I'm sure the RPMs are also low. EDIT 3: I should say that at just the right speed, the truck shakes alot. It's very noticeable in the cab. From some internet searching. Some ideas. Bent drive shaft, maybe. Alignment, I doubt it. torque converter in transmission, what?